Oof... the "sign in to confirm you're not a bot" thing actually hit a lot of the popular alternative frontends way earlier than when it was rolled out to main YouTube; it was actually one of the main reasons that made me drop Invidious. Sorry but I don't think I know if there is a direct workaround especially now that YT is quite sensitive about alternative frontends...
As others suggested, yt-dlp seems to always find a way, so if you don't mind downloading the videos locally and/or use mpv to stream them that is always an option
Maybe also try asking on c/nostupidquestions?